1. Field of the Invention
The present invention relates to a temperature regulator and a recording apparatus, and more particularly to a recording apparatus having a recording head for recording with the heat generated by heating elements via heat exchange members for exchanging the heat with the recording heat attached thereto, wherein it comprises a temperature regulator for regulating the temperature of the recording head, and a recording head unit provided with the temperature regulator.
2. Related Background Art
An ink jet system, which is included in the recording system for recording by the use of heat energy has various advantages, unlike other systems, such that it enables high-resolution and high-speed recording, and the recording head and apparatus can be constructed relatively inexpensively because recording heads with this system are manufactured in the same process as that for semiconductor devices.
By the way, in a recording apparatus for recording by the use of heat energy, it is commonly observed that heat accumulation occurs along with the progress of recording, and temperature distribution between recording elements is caused owing to the heat accumulation. The occurrence of heat accumulation and temperature distribution may effect the recording characteristic of recording elements, and result in such a problem that density irregularities occur in a recording image, or color balance is disturbed for the color recording.
Such heat accumulation should be considered particularly in an ink jet recording apparatus for recording with ink. That is, some part of the heat energy generated by electro-thermal converters during the recording is used for discharging the ink by causing the state of the ink to change. Another part thereof is transferred to the ink within liquid channels and common liquid chamber. Further, still another part of the heat is conducted to the substrate side where electricity-heat converters are disposed. With such heat transfer, the temperature of ink within the liquid channels and common liquid chamber is varied, thereby correspondingly causing the distribution of ink temperatures between discharge ports.
The variation of ink temperature and other factors may effect the viscosity of ink etc. That is, the ink viscosity in a higher temperature region is made lower than that in a lower temperature region. As a result, the quantity of ink discharged from each discharge port is changed, so that the densities of pixels to be recorded are changed. In this case, if there is some temperature distribution of ink between a plurality of discharge ports, irregularities of density may occur in the recorded image, corresponding to that distribution. For a color image, the color balance may be disturbed.
Such an unevenness of density or color balance which may be caused due to heat accumulation is a conspicuous phenomenon in the full-line type recording head in which a plurality of discharge ports are arranged for recording of one line corresponding to the width of recording paper (e.g., if a recording paper of A3 size is used, 4376 discharge ports and corresponding electricity-heat converters are provided for a recording density of 400 dpi.). Thus, when many discharge ports are arranged, there is a possibility that the temperature distribution may occur between discharge ports due to differences between discharge frequencies of discharge ports. In addition, when the A3-size recording is performed immediately after the B5-size recording is performed using a part of the array of discharge ports, the temperature distribution may occur between discharge ports already used for recording and those not used.
Also, when a plurality of recording heads are used for each color ink in the full-color recording, the temperature differences between recording heads may occur due to the differences between use frequencies of recording heads, causing the dispersion of ink viscosities and thereby slight difference in the volume of ink discharged, so that the color balance is made uneven or ink densities may be different in ink colors.
In order to reduce the temperature distribution between discharge ports of a recording head or the temperature differences between a plurality of recording heads, the present inventor has proposed a arrangement in which heat exchange member such as heat pipe is attached to recording head to exchange the heat via the heat pipe.
In this arrangement, the heat pipe is provided with working fluid such as water within its hollow interior, in which heat exchange (radiation from recording head or heating of recording head) is performed by the working fluid evaporating or condensing depending on the temperature relative to the recording head. The inside of the heat pipe is filled with the working fluid and its vapor evaporated therefrom, and by the rapid heat transfer of vapor, the heat pipe is always subjected to the action for equalizing the temperature.
In order to promote the heat exchange by means of the heat pipe, the present inventor has also proposed a heat exchange device such as fins for performing the heat exchange (radiation) positively to the atmosphere or a fan for sending the air and provided in a portion to which the heat pipe extends, or a constitution for performing the heat exchange (heating the heat pipe) with the heat pipe by means of heater provided on a predetermined position of the heat pipe.
However, the heat exchange member as above described and the recording head attached includes following possible improvements as described below, in connection with heat exchange member itself and a recording head unit constitution using the heat exchange.
That is, the improvement in the efficiency of heat exchange using the heat exchange member such as heat pipe can reduce rapidly the temperature differences between discharge ports in recording head or between recording heads, thereby providing not only the high-speed recording without unevenness or density, but also the higher speed and improved precision of the head temperature regulation and control for controlling the temperature of recording head within a predetermined range. Further, as the heat exchange efficiency is improved, the effects can be obtained such that the size of the heat exchange apparatus can be made smaller.
In such heat exchange apparatus, main portions contributing to the improvement of its efficiency are a region where the heat pipe as previously mentioned performs heat exchange with the recording head, a region where fins are provided in the heat pipe to radiate the heat to the atmosphere, and a region where a heater is provided in the heat pipe. It is particularly important to operate the heat pipe itself efficiently. The working fluid and its vapor evaporated therefrom are filled in the heat pipe and associated passages, in which the heat exchange with the subject is made using either the evaporation of working fluid or the condensation of its vapor.
In a conventional heat pipe, for example, in order to promote the movement of working fluid within the heat pipe, channels should be provided in its internal wall, but a problem arose such that the processing of heat pipe would be more complicated.
Also, in the conventional heat pipe, a problem existed that the heat radiation with the vapor in heat exchange unit only for radiating the heat might effect the temperature of the other heated radiation units, thereby reducing the efficiency of heat exchange in the heat pipe.
The region where the fan is provided in the heat pipe is also important. This region is one in which the radiation efficiency is to be improved, but there are some cases where full advantage cannot be taken of the fan, and particularly, in a situation where the heat radiation is promoted by the air flow around the fins occurring by means of the fan, the feature of the fins can not be fully exploited.
That is, there was a problem that the air flow may not reach some fins, and so sufficient heat radiation can not be effected from those fins.
There are some instances of requiring smaller fins because of small-sized apparatus, thereby the radiation efficiency of the fins must be increased by the sufficient use of the feature for the fins.
Moreover, when a plurality of recording heads are used, such as in a recording apparatus for full-color recording, the heat exchange member as above described is provided for each recording head.
In such a case, in order to control the temperature of each recording head via the heat exchange member, a heater as a heating element or temperature sensor as temperature sensing element must be provided for each heat exchange member. As a result, the apparatus for the temperature control is made more complicated and expensive.
The present invention is to resolve the above-mentioned conventional problems associated with the heat pipe and peripheral portions thereof, wherein an object of the invention is to provide a recording head unit and a recording apparatus capable of performing efficient heat exchange by fully exploiting the features of a heat pipe comprising a portion filled with the working fluid and a portion filled with the vapor, which are separated by a partition plate.
Also it is an object of the present invention to provide a temperature control device, a recording head unit and a recording apparatus capable of improving the heat radiation efficiency all over the fins, in which the fins attached to heat radiation portion of heat pipe are provided with slits and slit plates for introducing a part of the air flow around the fins to the slits, thereby creating a turbulent flow state around the fins and increasing the whole area of fins with the slit plates.
Further, it is an object of the present invention to provide a recording apparatus capable of controlling the temperature of recording head with a simple constitution, in which the heat change members provided corresponding to a plurality of recording heads communicate with one another at predetermined portions and are formed integrally, and temperature sensing element and heating elements are provided in the vicinity of an integrated portion of the heat exchange members.
Also, it is another object of the invention to provide a temperature regulator, a recording head unit and a recording apparatus capable of controlling the temperature in accordance with the temperature of individual recording heads corresponding to each of the heat exchange members, even if the integrated heat exchange members as above described are used.
On the other hand, in an ink jet recording apparatus comprising the recording head as above described, the ink is discharged through discharge ports 5 with the pressure caused by bubbles generated in the ink in contact with elements 3 by the heat from heating elements, whereas in the recording head as above described, the amount of heat transfer to the heat pipe or heat exchange means becomes so large (because the thermal resistance of the heat pipe 2 is small) that the quantity of heat necessary to generate bubbles is insufficient in the heating elements 3, and the ink may not be discharged as fine liquid droplets.
As the heat flux transferred to the heat pipe is concentrated immediately below the heating elements, it is possible that the heat flux exceeding a critical amount of heat transport may flow into the heat pipe, thereby causing an abrupt temperature-up of recording head.
Further, for example, for attachment of the heat pipe to the apparatus, it is preferred that a region where fins are provided in the heat pipe is normally placed away from the area where the recording head is disposed, taking into consideration the effects of the air flow in discharging the ink with the recording head. In this region, high possibility exists that the air flow passing into or out of the fins may be obstructed by the other members constituting the recording apparatus, and particularly, in the small-sized recording apparatus which is one of the recent trends, it is sometimes difficult to lay the fins in a sufficient amount of air flow. Also, when a fan is provided to send the air to the fins, a position for disposing the fan is limited within a certain range by the relation with other members within the recording apparatus, and thereby, the direction or range of air flow is also limited.
On the other hand, in the recording apparatus, the constitution for moving a recording head unit is provided to perform the capping operation for discharge recovery process by supporting integrally the recording head unit composed of recording head and heat pipe.
In such movement, if the recording head and the heat pipe are ill balanced in supporting, a problem may arise such that a relatively large vibration may occur therein, causing the working fluid to be maldistributed within the heat pipe, and an unnecessary load may be applied to driving mechanism for the recording heat unit.
An object of the present invention is to consider and resolve conventional problems as above described, and thereby to provide a recording head unit and a recording apparatus capable of maintaining a stable recording characteristic of the recording head so that the appropriate heat exchange is enabled between the recording head body and the heat exchange means.
The present invention is based on the viewpoints of the heat radiation efficiency and the operation of recording head as above described, and it is an object of the invention to provide a recording apparatus capable of improving the heat exchange efficiency in heat exchange member and making the operation of recording head unit smoother, by application of the present invention to a supporting constitution for the recording head unit.
In addition, in a recording apparatus, such as a color ink jet recording apparatus using the full-line type head, comprising a plurality of ink jet recording heads with the ink discharge ports arranged over the entire width of recording for a recording medium, and the heat pipes as heat exchange means each for exchanging heat with each recording head and provided in contact with almost the whole area along the longitudinal direction for each recording head, the heat pipe is secured onto a side face of each of the recording heads provided in parallel and spaced by a predetermined distance for each other, whereby the spacings between recording heads and the relative positions in the longitudinal direction must be retained precisely with high accuracy. Especially, the spacings between recording heads can affect the capacity of memory involved in recording, and as they should be desirably as little as possible for small-sized recording apparatus, the registration between recording heads is difficult, whereby a problem arises as to how it is accomplished with high accuracy.
As the length of each recording head is great in the direction where discharge ports are arranged, some warpage or distortion may occur in the longitudinal direction, and if the recording is performed in the condition where the warpage exists, a recorded image contains the distortion as shown by broken lines in FIGS. 12A-12C, which may damage the recording quality significantly.
An object of the present invention is to consider and resolve the above-described problems, and thereby to provide an ink jet recording head unit and an ink jet recording apparatus capable of making the fine adjustment of the location in the longitudinal direction for each recording head and/or in the spacing between heads, and the amount of warpage, while heat exchange means are connected and retained therein.
Moreover, as it is common that the recording head and the heat exchange member are securely adhered, the exchange of recording head which is necessary, for example, when the ink is not sufficiently discharged from any one of a plurality of discharge ports, requires the exchange of heat pipe, which will lead to an increased cost of exchange. Also, in the arrangement where the heat pipe must be exchanged as one-piece, the operation for exchange may be sometimes relatively complicated.
On the other hand, in a so-called full-line type recording head, as there are relatively many heating elements, those heating elements are differently deteriorated so that the probability of failure is greater. Thus, the exchange of recording heads is premised to a certain degree on the use of recording apparatus with a full-line type recording head.
The present invention is based on the above-described view-points, and it is an object of the invention to provide a recording head unit and a recording apparatus having a constitution in which recording head and heat exchange member are detachable from each other by means of a biasing member having elasticity.